He's got two conservative SC judges appointed, quite possibly a third this term. He's got a ton of appellate court judges appointed. He scrapped the horrible Iran deal. He's increased energy production, and cut regulations. And as you said, the economy is doing well. There's a lot more for conservatives to like than just the tax cut.
As for the lack of more legislative accomplishments, who should Republican voters blame for that, Trump or Congressional Republicans? It makes more sense to blame the latter, but those are the very people you think should be saying Trump was the mistake.